Quantifiable differences between chartered accountancy firms are often found on the basis of size rather than between individual firms. In general, the Big Four offer more international opportunities, household-name clients, more structured training, the chance to specialise in particular industries � Smaller firms usually market themselves on factors such as greater client contact, greater variety of work (shorter audits at smaller clients), early responsibility, work-life balance, friendliness and smaller audit teams. In the end, graduates often choose between similar types of firm on the basis of the company culture and atmosphere, which often boils down to which of them seemed the friendliest at interview!
The interviewer will have expected you to have done your research on the firm � not just reading the careers section of their website but looking at the pages for clients, press releases etc. You should also look in the general business press for mentions of larger firms. Factors you could mention include: